Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations (which already declare read-only, idempotent, non-destructive) by disclosing concrete behavioral traits: no network access, no stored state, deterministic output, passwords never echoed, repeated query keys returned as arrays, and hard limits (64 KB input, 1 s per call, 1 MB result). These are exactly the operational constraints an agent needs before calling.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose is front-loaded and the 'Cuándo / No para / Efectos secundarios / Determinista / Límites' structure is easy to scan. But the content is duplicated in Spanish and English, the English text is largely repeated from inputSchema.description, and the 'when' list is padded with loosely related examples, inflating length without adding selection value.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return fields need no prose explanation, and limits, determinism and side effects are all stated. The one gap is error behavior: it never says what happens when the URL is not absolute, malformed, or exceeds 8192 characters, which matters for a single-input parser.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Only one parameter and schema coverage is 100%, with maxLength, an example, and a description in the schema, so the baseline is 3. The prose restates the same facts ('absolute URL') and adds no syntax or edge-case detail (e.g., what happens to relative or malformed input) beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: parses an absolute URL with the WHATWG parser and enumerates the outputs (scheme, host, port with default, path, query params as arrays, fragment, origin). It explicitly names the sibling it is not (url-build), so an agent can separate parse from construct without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides an explicit 'Cuándo' section and an explicit 'No para: construir una URL desde una base ... (url-build)' exclusion naming the alternative. The trigger list is diluted, however: claiming the tool applies to 'un token, una versión, un rango de IP, un documento HTML' is questionable for a URL parser and could mislead an agent into calling it on non-URL input.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.